We will develop a new dual-modality cerebrovascular imaging instrument, combining both computed tomography (CT) and single photon emission computed tomography (SPECT), for improved diagnosis of stroke. Simultaneous measurement of CT and SPECT will be used for structural and functional correlation which results in improved quantification of radionuclide uptake in comparison to SPECT alone. More detailed anatomical information can be obtained by acquiring a CT image that is co-registered with the SPECT data, compared with CT data alone. The proposed imaging system will incorporate new solid state detectors, combined with scintillators, and new integrated circuit signal-processing technology, which will offer superior imaging quality in a portable instrument for rapid stroke assessment in the ambulance or emergency room setting, or for follow-up patient assessment in the critical care unit. In Phase I, we will develop small arrays of new silicon photodiodes, with a range of pixel sizes, for use in each of the CT and SPECT detectors. The new photodiodes will be characterized with CdW0O and Csl(TI) scintillators for CT and SPECT, respectively, with conventional electronics. A commercially available application specific integrated circuit (ASIC) and a dual-mode ASIC developed by our UCSF collaborators will be evaluated for use with the CT/SPECT system. The Phase II project will include optimization of the silicon photodiodes, design and fabrication of optimized integrated circuits for signal processing, fabrication and assembly of prototype array modules, and testing of the prototype modules in an imaging application with radioisotope-filled phantoms. The results of the Phase I feasibility studies will determine whether the new photodiode designs will require modification for use with the CdWO4 and Csl(TI) scintillators, which of the ASICs is optimal for use in this application, and what types of modifications/improvements are required in the ASIC for the Phase II work. PROPOSED COMMERCIAL APPLICATIONS: In Phase III we will commercialize single and multiple detector modules based upon the Phase I and Phase II efforts, for clinical use in cerebrovascular CT/SPECT imaging instruments. A single silicon photodiode design will be used with different scintillators for x-ray and radionuclide imaging to achieve improved performance characteristics, more rapid diagnostic capability and reduced cost for CT and SPECT. The silicon photodiodes and signal-processing electronics are based on low cost reliable silicon planar processing techniques. In addition, the low cost silicon photodiodes can replace their expensive PMT counterparts which are extensively used in other SPECT and PET applications.